This invention relates to the field of detection and monitoring of vapors and gases. In particular, it relates to the field of detection and monitoring of toxic gases and vapors in industrial environments. A wide variety of hazardous substances are utilized in industrial manufacturing and processing, some of which give off gases and vapors of the toxic variety in ambient air in areas both internal and external to the industrial facility.
In order to protect workers from the effects of exposure to these hazardous substances, and to study their acute and chronic effects, it is useful to monitor the air which such workers breathe during the periods in which they are in the vicinity of these hazardous substances in order to determine and document the contaminant concentrations.
An example of the type of industrial applications which require toxic gas and vapor monitoring is the manufacture of polyurethane foam. In the manufacture of polyurethane foam, toluene di-isocyante (TDI) is utilized. Workers who inhale excessive TDI concentrations will experience respiratory irritation and sensitization. Serious adverse effects to such exposure are only now coming to the attention of medical safety researchers. The literature indicates that these effects occur at low exposure levels.
Other toxic gases or vapors present similar safety problems including phosgene, chlorine, hydrogen sulfide, nitrogen dioxide, vinyl chloride and sulfur dioxide.
Known sampling techniques for detecting levels of toxic gases to which workers are exposed have not been satisfactory. A particular problem is that high peaks of brief exposure do not show up. There is evidence to suggest that high excursions of short duration may be a significant factor in assessing the effect of the toxic substance on the worker.
A recent development in the field is a portable miniaturized monitor which exposes a roll of gas sensitive chemically treated tape in the breathing zone of a worker. This device is the subject of a co-pending patent application Ser. No. 567,379 filed Apr. 11, 1975, by the present assignee and hereby incorporated by reference. Upon exposure, a stain develops upon a portion of the tape which is later read on a readout device such as presently disclosed. Since reading of the tape occurs after exposure, the monitor includes means to prevent contamination of adjacent layers of tape. After a worker's shift is ended, the exposed tape is removed from the monitor and placed into the reader recorder to produce a permanent, graphic display of concentration versus time and total dose values. From this information, a time-weighted average exposure level as well as excursions above a predetermined maximum ceiling can be determined.
Reference is made to the U.S. Department of Labor, Occupational Health & Safety Administration publication, Job Safety & Health, Volume II, No. 11, for additional background on the subject of monitoring TDI and other toxic gases.